Many disc drives today use a transducer formed of two elements. A first element is a thin film head that is used for writing information representative of data to the surface of the memory disc. A second element is a magneto resistive element or giant magneto resistive element (“MR element”) that is used to read information representative of data from the surface of the memory disc. The resistance of the MR element changes in the presence of a magnetic field so the MR element is used to sense transitions on the disc that have been previously written with the thin film write element. The transducer is typically housed within a small ceramic block called a slider. The slider is passed over the rotating disc in close proximity to the disc that includes magnetic transitions representative of data.
The process of forming individual sliders starts with forming multiple transducers on a surface of a ceramic wafer using semiconductor fabrication techniques. After forming the transducers on the wafer, the wafer is then sliced or cut to form an elongated bar having a row of transducers (a rowbar). MR elements include an MR stripe. The resistivity of the MR element is a function of the stripe height. As a result, manufacturing includes removal of material to produce a stripe height that produces a head with a certain specified resistivity. During manufacture, the elongated rows of transducers are placed in carriers and initially lapped to smooth the surface and provide a first “rough approximation” removal of material.
After lapping, the elongated rows of transducers are placed in a vacuum chamber and ion milled. Ion milling removes material at a slower, more controlled rate than the lapping process. Ion-beam etching or ion milling is a physical process. The wafers are placed on a holder in a vacuum chamber and a stream of argon is introduced into the chamber. Upon entering the chamber, the argon is subjected to a stream of high-energy electrons from a set of cathode (−) and anode (+) electrodes. The electrons ionize the argon atoms to a high-energy state with a positive charge. The wafers are held on a negatively grounded holder. The grounded holder attracts the ionized argon atoms. As the argon atoms travel to the wafer holder they accelerate, picking up energy. At the wafer surface they crash into the exposed wafer layer and literally blast small amounts from the wafer surface. Scientists call this physical process momentum transfer. No chemical reaction takes place between the argon atoms and the wafer material. Ion beam etching is also called sputter etching or ion milling.
This manufacturing process has problems. The initial steps of forming the MR elements using semiconductor fabrication techniques does not produce MR elements having uniform stripe heights. The removal of material from the sliced wafer or row of ceramic material, both by lapping and by ion milling, removes about the same amount of material from every MR element associated with a row of MR elements. The result is that the resistivity of the MR elements varies across the row of MR elements sliced from the ceramic wafer. In other words, the methods for removing material from a row of MR elements held on a holder treats each MR element in the row uniformly resulting in a wide distribution of stripe heights and a wide distribution of resistivity associated with the individual MR elements across the row of MR elements.
The semiconductor processes for removing materials generally treat the entire surface of a substrate uniformly. Generally, if more material is to be removed from one portion of a surface than another, the portion of the surface that is not to have more material removed is covered with a mask. Making structures using semiconductor techniques requires that a series of masks be laid down or used to cover certain portions of a substrate while additional materials are removed or added to form the structure. Generally, there is no way to move the mask during a semiconductor process. After one process is complete, the old mask is removed and a new mask is placed thereon to add material or remove material to form the structure.
Still another problem associated with the manufacturing process is that feedback as to the stripe height or resistivity of the MR element is not obtained during manufacture.
What is needed is a method and apparatus that can be used to carefully control the stripe height dimension of individual MR elements within a row of MR elements. Since the resistivity of the MR element is related to the stripe height, if each MR element is carefully controlled, the signal output of each MR element can be carefully controlled to have values within a selected range. The MR elements can also be controlled so that the deviation amongst the population of the individual MR elements is small. There is also a need for a process that uses feedback to control the stripe height and resistivity of the MR element during manufacture. If the dimensions or the stripe height dimension of the MR element can be controlled, MR elements can be reliably manufactured that will operate so that transitions written very closely together, such as at a very high areal density, may be detected or read. What is also needed is a method and apparatus that is both reliable and quick, such that it can be used to produce MR elements.